Process of making ferrophosphorus.



JOHN JEFFERSON GRAY, JB.,

0]! ROCKDALE, TENNESSEE.

PROCESS OF MAKING FERROPHOSPHORUS.

Specification of Letters Patent.

Patented Mar. 27, 1917.

No Drawing. Continuation of applieationSerial No. 106,005, filed .Tune 26, 1916. This application filed December 28, 1916.

To all whom it may concern:

Be it known that I, JOHN JEFFERSON GRAY, J r., a citizen of the United States, residing at Rockdale, in the county of Maury and State of Tennessee, have invented certain new and useful Improvements in Processes of Making Ferrophosphorus; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to processes for producing fcrro-phosphorus and has for one of its objects to improve the process disclosed in my prior Patent #831l27, dated Septenr ber 1s, 1900.

With this and other objects in view the invention consists in the novel steps and combinations of steps constituting the process, all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

In order that the precise invention may be clearly understood it is said 1- In my said Patent #831427, I have referred to various processes of producing lerro-phosphorus and l have also disclosed a blast furnace method of producing the same from natural phosphates.

This invention differs from the process of my said patent in that it utilizes predetermined top and bottom temperatures in the furnace. as well as a limited supply of preheated air It provides an excess of carbon in the fusion zone, and localizes the limits of said zone; it lays emphasis on the physical and mechanical conditions of the charge materials and the free circulation through the same of the ascending gases; it employs a slower downward movement of the charge materials in the furnace than is customary in ordinary blast furnace practice: and it provides for cleaning out at intervals without disturbing the continuous production of ferro-phosphorus, the sticky accumulatitms that collect on the hearth which are probably due to highly refractory materials containing aluminum and other elements existing as impurities in the charge.

The following may be considered as an example of a charge that is llsl illly made up Serial No. 139,387.

in carrying out the process for the production of ferro-phosphorus containing over 20% phosphorus.

Silica. sand or flint:

Total Coke, as carbon, C

It is well known in blast furnace practice that the carbon monoxid, CO, present in the ascending gases effects what is termed an indirect reduction of a portion of the iron ore to metallic iron when the proper temperatures are maintained in the stack. This indirect reduction will take place when the temperatures are as lOl' as say 450 F. It is further well known that elemental phos phorus, P, will enter reduced iron to form iron phosphids at temperatures of say a low red heat. Therefore, in carrying out an economical and commercially efficient process of making ferro-phosphorus it is desirable to provide as large a zone as possible for the iron and to afford as full an opportunity as possible for the elemental phosphorus to enter said reduced iron. Accordingly. one of the features of this invention resides in the fact that the top temperatures of the stack are maintained at say not higher than 450 F. or 500 F., thus affording a maximum zone in the stack for the indirect reduction of iron.

In order to secure a maximum penetration of the phosphorus into said reduced iron, as much elemental or free phosphorus should be provided in the ascending gases as is possible. But a maximum quantity of free phosphorus in the gases will depend upon a proper manipulation of the bottom temperatures, as will now be made clear.

That is to say, should the temperature of the fusion zone of the furnace be too low the reactions producing the slag will be incomplete, more or less phosphorus will be lost in the slag, and'an insufficient quantity of phosphorus will be liberated into the ascending gases. The furnace would also build up on the bottom, run cold, and gradually chill to the clogging point. On the other hand, if one should admit too much air into the furnace in an attempt to increase the temperature of the fusion zone, owing to theabnormally refractory character of the charge, the temperature would be likely not to increase at all, but the carbon would ignite higher up in the stack, and thus the fusion zone would be extended even above the water jackets, and cause well known troubles not necessary to mention.

In addition to the above, an excess of oxygen would accompany the admission of too much air, and would have the effect of reducing the quantity of free incandescent carbon in the fusion zone, and this deficiency of free carbon would have the further effect of limiting the .quantity of free phosphorus in the ascending gases, as will presently appear. On the other hand, if the temperature of the fusion zone is carefully regulated as disclosed below, a maximum quantity of free phosphorus will appear in the ascending gases and will enter the above mentioned indirectly reduced iron, all the way from the fusion zone to the top of the furnace, and thus a large percentage of ferro-phosphorus will be actually produced in the charge before the latter reaches the fusion zone at all. It is an important feature of this invention that this process accomplishes these desirable results, and the latter also distinguishes the same from the ordinary blast furnace process of making pig iron.

This invention, furthermore, efficiently utilizes an excess of carbon in the charge, and so manipulates the same as to produce a maximum quantity of ferro-phosphorus in the gases, as will now be made clear. That is to say, at the temperatures of say from 2500 I .to 3100 F.,maintained in the fusion zone of this furnace, the carbon and silica present will have the efiect of liberating oxids of phosphorus from the phosphate rock and especially phosphoric anhydrid P 0 Should there be no excess of carbon in the fusion zone, this said P 0 would ascend with the gases evolved, and as it has no power to enter the reduced iron present, it would either escape with theexit gases and thus be lost to the process, or else it would unite with a portion of the iron oxid Fe,O to form iron phosphate Fe P O a compound which cannot be reduced by CO gas. Therefore, should this said iron phosphate be allowed to form to any extent owing to a deficiency of carbon in the fusion zone, it will descend to the said zone and be reduced by the free carbon there present, and thus it would entail a further loss of carbon. In order-to avoid these disadvantages, I not only provide an excess of carbon in the fusion zone sufficient to reduce the P 0 as fast as it is evolved, but I further restrict the limits of the fusion zone by limiting the quantity of air fed to the furnace, and thereby maintain a sufficient excess of carbon therein under all conditions.

As just stated above, should too much air be admitted to the furnace the temperature would probably not rise and other evil results would follow. On the other hand, unless a sufficient temperature is maintained in the fusion zone, the formation of the above maximum quantity of free phosphorus would not take place. Therefore, in order to avoid an excessive admission of air to the furnace while at the same time maintaining the necessary bottom temperature in the As stated above, the physical and me-.

chanical conditions of the charge are of importance in carrying out this process, and in order to utilize the same to advantage, I preferably employ a coke of a firm texture as contradistinguished from a coke of soft texture. The former does not crush under the weight of the stack as does the soft coke, and therefore it does not as readily react with CO to form an excess of CO gas in the stack, but descends in a larger measure to the fusion zone to maintain the excess of carbon there employed. Not only does hard coke possess the above advantages over soft coke, but in addition, it more effectually absorbs than does soft coke the free phosphorus that has not entered the indirectly reduced iron above the fusion zone, and carries it down to or near said zone to be there liberated and later absorbed by the free iron during its second ascent.

I also preferably see that the charge is substantially devoid of finely divided material so that there is a free passage of gases between ,the individual particles and therefore, that the ascending elemental phos phorus shall have ample opportunity to enter the indirectly reduced iron before the fusion zone is reached. It will be observed that a free permeation of the interstices of the charge by the ascending gases is more important in this process than in a pig iron process, because in this process not only is it necessary to get a maximum contact between the GO present and the particles of the iron, but it is also important to get a maximum contact between the free phosphorus present and the reduced iron, when it is above a particular temperature, which is not the case in a pig iron process.

In addition to the above, this process differs from my said prior patent as well as from pig iron practice in that after a large percentage of the iron in the charge has been thus indirectly reduced and has been penetrated by the ascending free phosphorus, the said iron mixed with the phosphate rock and silica reaches the fusion zone as a very refractory charge, because no reaction has as yet taken place between th relatively large quantities of descending phosphate rock and silica present. In pig iron practice no such large quantities of refractory material are thus brought directly into the fusion zone, and accordingly, if pig iron practice were followed, the furnace would chill and clog up. In this process, on the other hand, by providing the above excess of coke, I readily cause a decomposition of the phosphate rock, I liberate its phosphorus and a large portion of its oxygen and therefore, I leave the calcium free to combine with the silica and other bodies present, so that notwithstanding the abnormally large quantites of refractory material brought to the fusion zone, it is readily furnaced and no clogging results. Owing to the refractory character and quantity of the material thus brought to the fusion zone, the reactions takin place in this furnace require time, and therefore, should one urge the charge through the furnace with the same celerity with which he is accustomed in pig iron practice, incomplete reactions would follow, a large proportion of the phosphorus would be lost in the slag, relatively small quantities of iron phosphid would be recovered and considerable quantitles of P 0 would be wasted as such. In addition to this, a speeding up of the stock would cause the furnace to gradually run cold and clog up. Therefore, one should be careful not to adopt the same speed of stock through the furnace in carrying out this process as he is-accustomed to in the pig iron practice.

When the charge reaches the fusion zone the unreduced iron is directly reduced, and as there is an excess of free phosphorus in said zone, this directly reduced iron is immediately permeated in said zone with phosphorus so that the ferro-phosphorus collects on the hearth very much after the manner of tions. This accumulated mass often follows the use of charges wherein the excess of carbon is'not high. When the excess of carbon is high, however, the trouble is likely to disappear. When it does occur, I find it convenient at regular intervals to follow the phosphate charges with ordinary pig iron charges. That is, after admitting to the furnace say four or five ferro-phosphorus charges, I then admit to the furnace a normal charge of material for making pig iron consisting of iron ore, coke and lime stone. If the'accumulated mass is great on the hearth, I may increase the amount of coke that is usually employed with the pig iron charge to say double its normal quantity, while if the accumulated mass is not very great, less coke can be conveniently employed. The effect of employing these pig iron charges is to provide an excess of coke near the bottom of the fusion zone which there produces a high temperature and melts the said accumulated mass.

The oncoming downwardly descending pig iron charge material fluxes with said mass and it passes off with the pig iron slag. In the meantime the iron of the pig iron charge as well as the other iron present, unites with some of the phosphorus contained in the accumulated mass on the hearth to form ferro-phosphorus.

In addition to this, the downwardly moving iron in the pig iron charge receives a greater or less amount of phosphorus from a preceding phosphate charge and this said iron together with the directly reduced iron in the pig iron charge passes on into and mixes with the pool of molten ferro-phosphorus on the hearth, containing say 21% phosphorus, and although it dilutes to some extent said pool yet it does not very greatly alter the percentage of phosphorus. In this way, although the regular ferro-phosphorus charges are interrupted, yet, ferrophosphorus is nevertheless made from the pig iron charge, and therefore, the operation and outputof the furnace are rendered continuous.

Further, notwithstanding the fact that the iron of the pig iron charge dilutes to some extent the high grade ferro-phosphorus already made, and thus lowers somewhat its content of phosphorus, yet, this said iron increases the total tonnage of ferro-phosphorus produced by the furnace. Further, this dilution of the phosphorus content of the product is not a commercial disadvantage, because as a matter of fact, it .is less expensive to produce ferro-phosphorus of from 16% to 18% phosphorus content than it is to produce a higher content of phosphorus.

As a matter of fact, from a commercial point of view, it is often well to even add pig iron or other forms of metallic iron, such as scrap cast iron, directly to the charge and thus bring down the average content' of phosphorus in the pool because this will increase the tonnage produced.

It will now be clear that in order to attain the useful results of this invention one may provide a temperature at the fusion zone of say from 2200 F. to 3100 F., after having supplied a charge of the general character as that above mentioned. That he should then so regulate his air at the twyers that a temperature of say not over 550 F. shall appear at thestock line regardless of the height of the furnace. The exit gases should be carefully examined to note any deficiency in carbonic acid gas CO and any excess of phosphoric anhydrid P 0 above what had been previously observed when a maximum production of ferro-phosphorus was had. When such deficiency or excess appears then the air supply, or the bottom temperature, or both should be alternately increased and diminished, until the exit gases show the right quantity of CO and the right deficiency of P 0 Under the best working conditions there should ordinarily appear in the exit gases about say 6% of CO and no appreciable or noticeable quantity of P 0 should appear therein at all. If this quantity of CO as begins to run down or becomes substantially less than 6%, it is an indication that a top temperature too high for the formation of CO is being employed, or that the proper reactions between the CO gas present and the oxygen compounds of the stock are not being had. Therefore, in such cases the quantity of the blast should be decreased and its temperature raised. Should a noticeable quantity of P 0 appear in the exit gases, it is an indication that too much air is being supplied through the twyers and that the fusion zone is not sufficiently localized to supply the necessary high temperature and the necessary amount of the free incandescent carbon to deoxidize all the P 0 evolved, and therefore, the amount of air supplied to the furnace should be cut down until the P 0 disappears from the exit gases. Then the yield of ferro-phosphorus should be a maximum or nearly so, but if it is not, and further manipulations of the air, its temperature and of the bottom temperature does not raise the efliciency of the articular furnace being operated, then the ailure will be found to be due to the charcharge or by increasing or decreasing the quantity of iron in the charge, being careful of course, to maintain a correct balance be tween the acids and bases and to maintain an excess of'c-arbon in the charge all as indicated above.

While I preferto use natural phosphates,

and especially tri-calcium phosphate rock as a source of phosphorus, yet, of course, other sources of phosphorus may be employed, among themthe well known basic slags of a high phosphorus content, such for example, as the well known Thomas slag, the Gilchrist slag, etc. In the employment of such slags, however, since they contain less phosphorus and more lime than does tri-calcium phosphate rock, for example, the stock reaching the fusion zone will require more silica to flux the same and will be even more refractory than in the case above discussed. Accordingly, a greater excess of carbon per pound of phosphorus present or per pound of ferro-phosphorus to be produced will be required. The exact proportions with the knowledge above disclosed will be readily ascertained by the skilled metallurgist.

While the top temperature should be maintained within about the limits above disclosed to produce the best results yet, ferro-.

phosphorus can be less efficiently produced by raising the top temperatures to any degree up to say 1350 F. provided sufficient carbon is present in the fusion zone, but I do not recommend such a procedure. In other words,experience has taught me that the iron present over a wide range of temperatures seems to have a decidedly advantageous effect in aiding in loosenin the chemical bonds binding the atoms, or c iemical radicals present in the phosphate rock, so that it is commercially practicable to liberate very much larger percentages of phosphorus in the charge than would be possible in a blast furnace were no-iron or its equivalent present, and therefore it is obvious that those skilled in the art may vary the details of the invention Without departing from the spirit thereof, and I do not wish to be limited to the above disclosure except as may be required by the claims.

What I claim is 1. The process of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixdescribed.

ture of iron bearing material, phosphatic material, fluxing material and carbon; maintaining free uncombined carbon in the fusion zone of the furnace; maintaining a temperature in said fusion zone sufficient in the presence of said free carbon to reduce the phosphorus of said phosphatic material to the elemental condition; and maintaining such atop temperature as Will facilitate the entry of the phosphorus into the iron present, substantially as described.

2. The process of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron ore, phosphate rock, fluxing materials and carbon; maintaining free carbon in the fusion zone of the furnace; maintaining a predetermined temperature above 2000 F. in the fusion zone of the furnace; and maintaining a predetermined temperature not higher than700 F. at the stock line of the furnace; substantially as described.

3. The process of producing ferro-phos phorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron ore, phosphate rock, fluxing materials and carbon; maintaining free carbon in the fusion zone of the furnace; maintaining a, predetermined top temperature near the stock line of the furnace; maintaining such a predetermined localized high temperature at the bottom of said furnace as will effect a reduction of the phosphate rock to elemental phosphorus, and which in connection with said top temperature will cause an indirect reduction of the descending iron ore from near the top to near the bottom of the furnace; substantially as described.

4. The process of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron' ore, phosphate rock, fluxing materials, and carbon; maintaining free carbon in the fusion zone of the furnace; maintaining a localized temperature in said fusion zone sufiicient in the presence of said free carbon to reduce the phosphorus of said rock to the elemental condition; and maintaining a predetermined low top temperature in said furnace, substantially as 5. The process of preventing" a dirty hearth in the making of ferro-phosphorus by blast furnace methods which consists in charging the furnace at suitable intervals with iron bearing material, phosphate rock, silica and an excess of carbon; smelting the same; and immediately following said charge with a charge of iron ore, basic material and carbon, substantiall-yas described.

6. The orocess of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron bearing material, phosphatic material, fluxing material and carbon; maintaining free carbon in the fusion zone of the furnace, maintaining a temperature in said fusion zone sufficient in the presence of said free carbon to reduce the phosphorus of said phosphatic material to the elemental condition by admitting a blast of preheated air to said zone; and maintaining a predetermined top temperature in said furnace, substantially as described.

7. The process of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron bearing material, phosphatic material, fluxing material and carbon; maintaining sufiicient free uncombined carbon in the solid state in the fusion zone of the furnace to decompose the phosphatic material and to reduce substantially all the evolved oxids of phosphorus; and maintaining a localized temperature in said fusion zone sufficient in the presence of said free solid carbon to effect said decomposition andreduction, substantially as described.

8. The process of producing ferro-phosphorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron ore, phosphate rock,'fluxing materials, and carbon; maintaining free carbon in the fusion zone of the furnace; maintaining a localized temperature in said fusion zone sufficient in the presence of said free carbon to reduce the phosphorus of said rock to the elemental condition by admitting to said zone a blast of air preheated to a temperature above 900 F.; and maintaining phorus in a blast furnace which consists in charging the furnace with a suitable mixture of iron ore, phosphate rock, fluxing materials, metallic iron and carbon; maintaining free carbon in the fusion zone of the furnace; maintaining a localized temperature in said fusion zone sufficient in the presence of said free carbon to reduce the phosphorus of said rock to the elemental condition by admitting to said zone a blast of preheated air; and maintaining a predetermined low top temperature in said furnace, substantially as described.

In testimony whereof I aflix my signature, in presence of two witnesses. JOHN JEFFERSON GRAY, JR.

Witnesses:

T. J. FULWELL, L. H. STANDIFER. 

